J . Med. Chem. 1989, 32, 1360-1366
1360
Novel Indolecarboxamidotetrazoles as Potential Antiallergy Agents' Paul C. Unangst,*,t David T. Connor,+ S. Russell Stabler,+Robert J. Weikert,+ Mary E. Carethers,+ John A. Kennedy,: David 0. Thueson,: James C. Chestnut,: Richard L. Adolphson,' and M. C. Conroyt Departments of Chemistry and Pharmacology, Parke-Davis Pharmaceutical Research Division, Warner-Lambert Company, Ann Arbor, Michigan 48105. Received September 9, 1988 The synthesis and antiallergic potential of a series of novel indolecarboxamidotetrazoles are described. A number of compounds inhibit the release of histamine from anti-IgE-stimulated basophilic leukocytes obtained from allergic donors. Optimal inhibition is exhibited by compounds with 3-alkoxy, 5-methoxy, and 1-phenyl substituents on the indole core structure. Compound 8d (5-methoxy-3-(l-methylethoxy)-l-phenyl-Nl~-tetrazol-5-yl-1H-indole-2carboxamide; designated CI-949) is a potent inhibitor of histamine release from human basophils and from guinea pig and human chopped lung.
Histamine, leukotrienes, prostaglandins, and other biologically active mediators, produced and released from mast cells, basophils, and eosinophils, have been implicated in the pathogenesis of asthma and other allergic diseases.2 The release of these mediators may be initiated by a variety of antigens or other immunologic triggers, which may explain the heterogeneous nature of the allergic patient population. Our lack of understanding of the relative importance of the various cell types and mediators involved has been a roadblock for the successful development of antiasthma drugs. In addition, an incomplete knowledge of the mechanisms of action of currently used drugs for asthma therapy (corticosteroids, disodium cromoglycate (DSCG), and the~phylline),~ as well as the lack of predictive preclinical in vivo model^,^ has hampered new drug development. DSCG, initially thought to be acting clinically by stabilizing mast cells,5 has been shown to inhibit the release of histamine only from selected mast cells (rat mast cells and, to a lesser extent, passively sensitized human lung cells). Mediator release from other types of mast cells or basophils is not inhibited by DSCG.6 The clinical failures7 of more potent compounds with activity in the rat passive cutaneous anaphylaxis (PCA) test (a profile similar to that of DSCG) have raised questions about the clinical mechanism of action of DSCG. We elected to pursue compounds that block the release of multiple mediators from human basophils and mast cells. As a measure of mediator release inhibition, compounds were tested for their ability to block histamine release from antigen-stimulated human basophils. This test model, as developed by Lichtenstein and other^,^,^ has been employed in the evaluation of potential antiallergy drugs of considerable variability in potency and efficacy,10-14 Inhibition of histamine release from guinea pig and human chopped lung was also evaluated for selected compounds. The antiallergic activity of a series of furo[3,2-b]indoles, including a description of the pharmacology of CI-922 ( l ) , has been previously reported.'"17 Structural modification of 1 led to a series of indolecarboxamidotetrazoles 2. The synthesis and biological evaluation of these compounds are described in this paper. Chemistry The overall synthetic sequence for the preparation of a series of indole-2-carboxamidotetrazoles 8 is shown in Scheme I. (Substituents R1-R, for 3-9 are listed in Table IV. All compounds with identical subscripts (a, b, c, etc.) have the same pattern of substituents.) Department of Chemistry.
* Department of Pharmacology. 0022-2623/89/1832-1360$01.50/0
N-N
arginine I
2
Alkoxyindole esters 5 were prepared by selective O-alkylation of enolic indole esters 3. Similar alkylation of N-substituted enolic indole esters 4 provided the related alkoxy esters 6 (methods A and B). Esters 3a, 3 t , 3x,3y, (1) Presented, in part, at the 192nd National Meeting of the Am-
erican Chemical Society, Anaheim, CA, September 7-11, 1986; MEDI 62. (2) (a) Kay, A. B. Eur. J . Respir. Dis. 1986, 69 (Suppl. 147), 38. (b) Raphael, G. D.; Metcalfe, D. D. Ibid. 1986,69 (Suppl. 147), 44. (c) Holgate, S. T.; Kay, A. B. Clin. Allergy 1985, 15, 221. (d) MacGlashan, D. W.; Schleimer, R. P.; Peters, S. P.; Schulman, E. S.; Adams, G. K.; Sobotka, A. K.; Newball, H. H.; Lichtenstein, L. M. Fed. Proc. Fed. Am. SOC.Exp. Biol. 1983,42, 2504. (3) (a) Barnes, P. J. Eur. J . Respir. Dis. 1986,623, (Suppl. 144), 217. (b) Church, M. K.; Warner, J. 0. Clin. Allergy 1985, 15, 311. (4) (a) Warner, A.; Abraham, W. M. Lung 1982, 160, 231. (b) Church, M. K. Agents Actions 1986, 18, 288. (5) Cox, J. S. G. Nature (London) 1967, 216, 1328. (6) Lichtenstein, L. M.; et al. In Asthma Physiology, Immunopharmacology, and Treatment; Kay, A. B., Austen, K. F., Lichtenstein, L. M., Eds.; Academic Press: London, 1984; pp 1-15. (7) Auty, R. M. Eur. J. Respir. Dis. 1986, 69 (Suppl. 147), 120. (8) Lichtenstein, L. M.; Osler, A. G. J . Exp. Med. 1964,120,507. (9) Siraganian, R. P.; Brodsky, M. J. J . Allergy Clin. Immunol. 1976, 57, 525. (10) Subramanian, N. Arzneim.-Forsch. Drug Res. 1986,36 (I), 502. (11) Yanagihara, Y.; Shida, T. Arzneim.-Forsch. Drug. Res. 1986, 36 (Iu, 1627. (12) Paul. R.: Brockman. J. A.: Hallet. W. A.; Hanifin. J. W.: Tarrant, M. E.; Torley, L. W.; Callahan, F. M.; Fabio, P. F.; Johnson, B. D.; Lenhard, R. H.; Schaub, R. E.; Wissner, A. J . Med. Chem. 1985,28, 1704. (13) Khandwala, A.; Coutts, S.; Pruss, T.; Jones, H.; Neiss, E.; Weinryb, I. Biochem. Pharmacol. 1987, 36, 663. (14) Conroy, M. C.; Kennedy, J. A.; Thueson, D. 0. Int. Arch. Allergy Appl. Immunol. 1985, 77, 222. (15) Unangst, P. C.; Carethers, M. E.; Webster, K.; Janik, G. M.; Robichaud, L. J. J . Med. Chem. 1984, 27, 1629. (16) Robichaud, L. J.; Stewart, S. F.; Adolphson, R. L. Int. J . Immunopharmacol. 1987, 9, 41. (17) Wright, C. D.; Hoffmann, M. D.; Thueson, D. 0.;Conroy, M. C. J . Leukocyte Riol. 1987, 42, 30.
0 1989 American Chemical Society
Journal of Medicinal Chemistry, 1989, Vol. 32, No. 6 1361
Zndolecarboxamidotetrazoles as Antiallergy Agents
Scheme I1
Scheme I
Meoaco2H -Meoac -
h a C02Meo H N"CN
I
H 3
H
C02Me
C6H5
12
11
I
I
R,+~JJ~"'
C6H5
c6HS
I
\
5
I
CsHS
4
-
N ~ C N
I
R2
C02Me
13
14
R2
6
15
CO2H
CO2H
I
I R2
R2
9
7
\
Table I. Intermediate Enolic Indole Esters C02Me
RIg)-JOH
L no.' 4n 4u
mtx "C 147-150 146-150 170-173
crvst solvent formula MeOH/HzO C18H17N06 Et20/hexane CI7Hl5NO4 42 C16H12C1N03 2-methoxyethanol/HzO 4dd 153-155 2-PrOH C17Hd04 R1and Rzare as defined in Table IV.
analysis C, H, N C, H, N C, H, N, C1 C, H, N
388, 4a, 4q, 4w, and 4bb were prepared as previously
de~cribed.'~~ Additional '~ esters (Table I) with a 1-phenyl substituent were prepared by fried lander'^^^^^^ procedure from the appropriate 2-(pheny1amino)benzoic acid. Reaction of the N-unsubstituted esters 50 and 5p with phenylmethyl bromide yielded esters 6r and 6s. Most of the esters 6 were oils or amorphous solids and were utilized crude for conversion to alkoxy acids 7 (Table 11) by saponification. Esters 5 were similarly saponified (methods C, D, and E). Alkoxy carboxylic acids 7d, 7 x , 7y, and 7aa and acids 9h, 9i, 9j, and 9m containing nonalkoxy substituents in the indole 3-position were prepared as previously described.lsVz1 In a few cases (7n,7bb, and (18) Unangst, P. C.; Connor, D. T.; Stabler, S. R.; Weikert, R. J. J . Heterocycl. Chem. 1987, 24, 811. (19) Unangst, P. C.; Carethers, M. E. J. Heterocycl. Chem. 1984, 21, 709. (20) Friedlander, P.; Kunz, K. Ber. 1922, 55, 1597. (21) Unangst, P. C.; Connor, D. T.; Stabler, S. R. J . Heterocycl. Chem. 1987,24, 817.
91) an analytically pure sample of the intermediate carboxylic acid could not be obtained, and the crude product was converted directly to the (carbony1amino)tetrazole. (Carbony1amino)tetrazoles 8 were prepared by reaction of 5-aminotetrazole and the coupling reagent 1,l'carbonylbis( 1H-imidazole) with carboxylic acids 7 and 9 (methods F and G). Hydroxy (carbony1amino)tetrazoles 8a and 8v were obtained by catalytic hydrogenolysis of the corresponding phenylmethoxy compounds 8f and 8w. Oxidation of methylthio derivative 8j provided the methylsulfonyl analogue 8k. The preparation of indolyltetrazole 15 is shown in Scheme 11. Nitrile ester 12 was obtained by esterification of nitrile carboxylic acid l l . I 9 Cyclization of 12 with base yielded the indole nitrile 13, and 0-alkylation of 13 yielded the alkoxy nitrile 14. Conversion of 14 to the desired tetrazole 15 was effected with tri-n-butylstannyl azide.22 Biological Results and Discussion Indolecarboxamidotetrazoles (Table 111) were synthesized with substituent variations on the indole benzene ring (R,) and at the indole 1-and 3-positions (R, and R3, respectively). Biological activity was initially assessed by the inhibition of histamine release from human leukocytes stimulated by anti-IgE antibody. Test results for the indolecarboxamidotetrazoles prepared are shown in Table IV. A number of compounds demonstrated potent inhibition of histamine release, and a preliminary structure-activity relationship could be discerned. When R, was 5-methoxy and R2 was phenyl (the same substituent pattern as that of the indole portion of l ) , an alkoxy substituent in the indole 3-position yielded analogues (8b, 8c, 8d, and 8f) with marked inhibitory activity. Replacement of the 3-alkoxy substituent with hydrogen (8h), isopropyl (8i), hydroxyl (8a), 4-nitrophenoxy (8g), or methylsulfonyl (8k) resulted in a loss of activity. Active compounds (Sj, 81, and 8m) were also obtained when the indole 3-position oxygen was replaced by sulfur. When R1 and R3 were kept constant as 5-methoxy and 1-methylethoxy, respectively, the desirability of a phenyl substituent on the indole nitrogen (R,) was evident. The N-phenyl analogue (8d) showed greater inhibition than the N-H (8p) or N-methyl (8q) compounds. Replacement of the 5-methoxy (R,) substituent with R, held constant as phenyl and R3 as 1-methylethoxy, in ~
(22) Sisido, K.; Nabika, K.; Isida, T.; Kozima, S. J. Organometal. Chem. 1971,33, 337.
1362 Journal of Medicinal Chemistry, 1989, Vol. 32, No. 6
Unangst et al.
Table 11. Intermediate Indolecarboxylic Acids
starting alkyl.b sapon.c enol ester method method vie1d.d % mD, "C crvst solvent formula analvsis A D 91 150 dec 4a B D 88 130 dec 4a 7ee 4a C' 36 241-242 E 7f 4a 89 123 dec E 30 230 dec 7g 4a E 147-150 70 3a 85 E 53 130 dec 7P 3a D 110-112 84 2-methoxyethanol/H20 7q 4q E 7r 3a 90 145-147 MeOH/H20 C i 7s 3a 68 128-130 EtOH/ hexane B E 7t 3t 66 128-131 t-BuOMe/ hexane E 7u 4u 85 113-115 Et20/hexane 7w 4w C 52 132 dec EtOAc/ hexane D 72 42 72 130 dec EtOAc/ hexane 7cc 4bb i 89 140-142 EtOAc/ hexane E 7dd 4dd 78 129 dec Et,O/ hexane " R1, Rz, and R3 are as defined in Table IV. *Examples of general alkylation procedures A and B are given in the Experimental Section. Examples of general saponification procedures C-E are given in the Experimental Section. dYield of unrecrystallized product. e Data shown are for the potassium salt of acid 7e. 'Heating time was extended to 18 h. gThe product was not recrystallized. "Calculated as the potassium salt hemihydrate. See the Experimental Section for specific procedure. j C: calcd, 62.64; found, 63.11. no." 7b 7c
Table 111. Indolecarboxamidotetrazoles
no." methodb yield, % mp, OC cryst solvent formula analysis 8a C 52 240 dec 2-methoxyethanol/H20 C17H14N603 C, H, Nd 8b F 40 235 dec DMF/HpO C18H16N803 C, H, N 8c G 80 226 dec 2-PrOH/DMF/H20 C1SH18N603 C, H, N 8d G 81 227 dec MeCN/HzO C20H20N603 C, H, N EtOAc C26H32N603 C, H, N Be F 45 203-204 F 54 212 dec DMF/H20 C24H20N603 C, H, N 8f 8g G 82 235 dec 2-methoxyethanol/H,O C23H17N705 C, H, Ne 8h G 84 271-274 MeCN/H20 C17H14N602 C, H, N 8i G 78 261-264 MeCN/2-PrOH C2OH2ON6O2 C, H, N 8j G 63 252-253 MeCN/2-PrOH C18H16N602S C, H, N 8k C 28 263 dec MeCN/2-PrOH/H20 C18H16N604S C, H, Nd 81 G 59 247-250 MeCN/2-PrOH C20H20N602S c , H, N, s 8m G 71 243-245 MeCN/2-PrOH C23H18N602S C, H, N, S 8n G 82 188- 190 MeOH/H20 C21H22N604 C, H, N 80 G 68 245 dec MeCN/DMF/H20 C13H14N603 C, H, N 8~ G 68 215 dec MeCN/H20 C14H16N603 C, H, N 8q F 72 223 dec 2-methoxyethanol/H,O C15H18N603 C, H, N 8r G 92 226 dec MeCN/H20 C20H20N603 C, H, N 8s G 85 212 dec f C21H22N603 C, H, N 8t G 82 254-256 MeCN/2-PrOH C20H20N603 C, H, N 8u G 68 205-208 MeCN/2-PrOH C20H20N603 C, H, N 8v C 74 243 dec MeOH/DMF/H,O C1SH18N603 C, H, Ng 8w G 72 205 dec MeCN/H20 C26H24N603 C, H, N 8x G 91 218 dec MeCN C20H2$J602 C, H, N 8~ G 92 235 dec f C19H17BrN602 C, H, N, Br C, H, N, C1 82 G 60 228 dec MeCN/H20 C1SH17C1N602 8aa G 68 240 dec MeOH/DMF/H20 CiaHi6C1zN60z C, H, N, C1 8bb G 74 203-205 MeCN/H20 ClSH18N602 C, H, N 8cc F 47 208 dec 2-methoxyethanol/H20 C23H18N602 C, H, N 8dd G 60 166 dec MeCN/2-PrOH C20H20N603 C, H, N a R1, Rz, and R3 are as defined in Table IV. *See general methods F and G in the Experimental Section. See the Experimental Section for specific procedure. Calculated as .H20. eN: calcd, 20.80; found, 20.16. 'The product was not recrystallized. BCalculated as .0.5H20.
general, resulted in compounds with activity inferior to that of 8d. The 5-phenylmethoxy (8w),5-chloro (82),and 5,6-dichloro (8aa) analogues did retain a reasonable level of activity, while the 6-methoxy ( 8 4showed reduced ac-
tivity compared to that of 8d, and the 4-methoxy analogue (8t) was inactive. Replacement of the (carbony1amino)tetrazole function at the indole 2-position with a direct indoletetrazole bond
Journal of Medicinal Chemistry, 1989, Vol. 32, No. 6 1363
Indolecarboxamidotetrazoles as Antiallergy Agents
Table IV. Inhibition of Histamine Release from Human Basophils by Indolecarboxamidotetrazoles
"-N H
I R2
no. 8a
8b 8c
8d
8e 8f
R1 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 5-Me0 4-Me0 6-Me0 5-OH 5-C6H5CHzO 5-Me 5-Br 5-C1 5,6-C12
R2 C6H5
CBH5 C6H5 C6H6
CBH5
R3
OH OMe OEt OCH(Me), OC9H1, OCHzCsHb O(4-NO2CsH4)
histamine release: % inhibition" 33 pM 10 pM hb 74 f 9 (5) 46 f 12 (5) 73 f 12 (5) 55 f 13 (5) 82 f 2 (45) 46 f 3 (43) C
84 (2) 43 (2) In. In. C6H5 H 8h CH(Meh In. 8i CsH5 C6H5 SMe 66 (2) 20 (2) 8j In. C6H5 S02Me 8k CBH5 SCH(Me), 50 f 4 (3) 13 f 2 (3) 81 8m C6H5 SC6H5 82 (2) 30 (2) 8n 4-MeOC6H4 OCH(Me)2 49 (2) 16 (2) 80 H OEt 46 (2) 7 (2) 8~ H OCH(Me)2 62 (2) 17 (2) 8q Me OCH(Me)2 45 f 13 (5) 18 f 6 (5) CH2C6H5 OEt 55 f 11 (3) 26 f 2 (3) 8r CH2C6H5 OCH(Me)2 69 f 17 (3) 61 f 28 (3) 8s CBH5 OCH(Me), In. 8t C6H5 OCH(Me)2 50 (2) 24 (2) 8u CBH5 OCH(Me)2 In. 8v CBH5 OCH(Me)2 66 (2) 65 (2) 8w In. C6H5 OCH(Me)z 8x C6H5 8~ OCH(Me)2 33 (1) 7 (1) C6H5 OCH(Me)2 72 f 9 (4) 18 f 8 (4) 82 8aa CBH5 OCH(Me)2 84 (2) 40 (2) 8bb H C6H5 OCH(Me)z In. 8cc H C6H5 OCHZCeH5 In. 8dd H 4-MeOC6H4 OCH(Me)z In. 15 37 (1) 25 (1) a Percent inhibition of basophil histamine release stimulated by anti-IgE. The standard error and (number of experiments) are shown. Inactive (In.) is defined as 125% inhibition a t a screening concentration of 33 pM. Sample fluorescence interferes with the histamine assay. 8l3
C6H5
CBH5
(compound 15) also resulted in reduced activity. In addition, none of the ester or carboxylic acid synthetic intermediates possessed significant inhibitory activity in the basophil test.23 Thus, to inhibit histamine release from human basophils, this series of indolecarboxamidotetrazoles must contain an alkylated electron-donating atom in the indole 3-position and be substituted in the 5- or 6-position with an alkoxy or halogen substituent. The 3-alkoxy, 5-methoxy combination appeared to yield the highest potency in blocking histamine release. Table V is a comparison of Sd, furo[3,2-b]indole 1, DSCG, and nedocromil, a more potent, second generation version of DSCG.24 In addition to the basophil assay, these compounds were also evaluated for their ability to inhibit antigen-induced histamine release from guinea pig and human lung mast cells. Compounds 8d was a potent inhibitor of histamine release in all three models. In contrast, nedocromil is a very weak inhibitor of histamine release from both dispersed lung fragments25 and basophils. The ability of 8d to inhibit leukotriene and thromboxane release from mast cells and neutrophils has also been reported r e ~ e n t l y . ~ ~ * ~ ~
Table V. Activity Comparisons in the Basophil and Chopped Luna Models basophil" guinea pig lungb human l u n g compound ICN, pM ICm FM ICm PM 8d 15.0 26.7 f 2.8 16.6 f 1.8 CI-922 8.5 13.4 f 1.4 DSCG Inc Ind In.d nedocromil In.' Insd In.d " Concentration of drug (pM) inhibiting anti-IgE-stimulated histamine release by 50% of control value. "oncentration of drug (pM) inhibiting ovalbumin-stimulated histamine release by 50% of control value. cInactive (In.) is defined as 125% inhibition at a screening concentration of 33 pM. dInactive (In.) is defined as 525% inhibition a t a screening concentration of 75 pM.
(23) Unangst, P. C. Unpublished results. (24) Gonzalez, J. P.; Brogden, R. N. Drugs 1987,34, 560. (25) Leung, K. B. P.; Flint, K. C.; Brostoff, J.; HudsDith, B. N.; Johnson, N. McI.; Pearce, F. L. Eur. J.Respir. Dis. 1986, 69 (Suppl. 147), 223.
(26) Adolphson, R. L.; Chestnut, J. C.; Kuipers, P. J.; Thueson, D. 0.; Wright, C. D.; Conroy, M. C. J. Allergy Clin. Immunol. 1988, 81, 232. (27) Stewart, S. F.; Conroy, M. C.; Wright, C. D. FASEB J. 1988, 2, A1604.
Conclusions A series of novel indolecarboxamidotetrazoles has been prepared. The preliminary antiallergic potential of these compounds was assessed by measuring inhibition of histamine release from human leukocytes stimulated by anti-IgE antibody. A number of compounds showed dose-related activity in this assay. The compounds with the best inhibitory potential contained 3-alkoxy, 5-methoxy, and 1-phenyl substituents on the indole core structure.
1364 Journal of Medicinal Chemistry, 1989, Vol. 32, No. 6
Unangst et al.
ester 4a," 6.96 g (0.050 mol) of anhydrous KzCO3, and 7.11 g (0.050 mol) of 1-fluoro-4-nitrobenzene in 90 mL of DMF was stirred and heated on the steam bath for 18 h. The mixture was cooled and added to 750 g of ice/H,O, and the product was extracted with CHzClz(3 x 200 mL). The combined organic layers were washed with H,O (2 X 300 mL), dried (MgSOJ, and evaporated to yield intermediate methyl ester 6g as an oil containing some residual Melting points were determined on a Mel-Temp or ElecDMF. trothermal capillary apparatus and are uncorrected. The 'H NMR Saponification of the crude intermediate ester 6g described spectra were determined at 90 MHz on a Varian EM-390, at 100 above by the procedure of method E yielded 6.1 g (30%) of MHz on an IBM WPlOOSY, or at 200 MHz on a Varian XL-200 carboxylic acid 7g. A sample recrystallized from aqueous 2spectrometer with tetramethylsilane as an internal standard. The methoxyethanol was analytically pure: mp 230 "C dec; IR (KBr) infrared spectra were recorded as potassium bromide disks on 1680,1490,1343,1218 cm-'; 'H NMR (CDC13)6 3.77 (s, 3 H, CH,), a Digilab FTS-14 or a Nicolet FT-IRMS-1 spectrophotometer. 6.63-7.67 (m, 10 H, A r m , 8.13-8.35 (m, 2 H, A r m . Anal. Elemental analyses were provided by the Analytical Chemistry (C2zH16N206) c , H, N. staff of this department. All new compounds yielded spectral 3-Ethoxy-5-methoxy-1 - ( phenylmethy1)- lH-indole-2data consistent with the proposed structure and microanalyses carboxylic Acid (7r). A suspension of 1.34 g (0.028 mol) of NaH were within *0.4% of the theoretical values unless indicated (50% suspension in mineral oil) in 50 mL of DMF was cooled in otherwise. an ice bath and treated dropwise over 20 min with a solution of Method A. Methyl 3-Ethoxy-5-methoxy-lH-indole-25.9 g (0.024 mol) of ester 50 in 50 mL of DMF. The ice bath was carboxylate (50). A mixture of 11.9 g (0.054 mol) of enol ester removed, and the mixture was stirred for 45 min and then treated 3a,lB8.0 g (0.058 mol) of anhydrous K2CO3, and 7.7 mL (9.1 g, with 3.4 mL (4.9 g, 0.029 mol) of phenylmethyl bromide. The 0.059 mol) of Et2S04in 150 mL of acetone was stirred at reflux mixture was stirred for an additional 20 h and then poured into for 16 h. The cooled mixture was added to 1.5 kg of ice/H,O, 1.0 kg of ice/H,O. The solid was filtered and washed with water and the precipitated product was filtered and washed with H,O. to yield 6.4 g (79%) of the intermediate methyl ester 6r, mp 57-59 Recrystallization from aqueous MeOH yielded 8.0 g (59%) of "C. analytically pure ester 50: mp 118-120 "C; IR (KBr) 3320, 1679, Saponification of 5.7 g (0.017 mol) of the crude ester 6r as 1483, 1032 cm-'; 'H NMR (CDCl,) 6 1.43 (t, 3 H, CH,CH,), 3.87 described in method E yielded 5.0 g (90%) of carboxylic acid 7r. (s, 3H, OCH,), 3.95 (s, 3 H, OCH,), 4.30 (q, 2 H, CH2CH,), A sample recrystallized from aqueous methanol was analytically 6.83-7.33 (m, 3 H, Arm, 8.47 (br s, 1 H, NH). Anal. (CI3Hl5NO4) pure: mp 145-147 "C; IR (KBr) 1674,1498,1228,1037 cm-'; 'H C, H, N. NMR (CDC13) 6 1.55 (t, 3 H, CH,CH,), 3.80 (9, 3 H, OCH,), 4.53 (Other alkylating agents employed with this procedure were (9, 2 H, CH2CH3),5.83 (s, 2 H, NCH,), 6.80-7.41 (m, 8 H, A r m , dimethyl sulfate, phenylmethyl bromide, and n-nonyl bromide.) 10.30 (br s, 1 H, C0,H). Anal. (C19HlgN04)C, H, N. Met hod B. Methyl 5-Methoxy-3-(1-methy1ethoxy)-15-Methoxy-3-(1-methy1ethoxy)-1-(phenylmethy1)-1Hphenyl-lH-indole-2-carboxylate (6d). A stirred solution of 24.8 indole-2-carboxylic Acid (7s). Alkylation of ester 5plS by the g (0.22mol) of t-BuOK in 100 mL of DMSO was cooled in a cold procedure described in the preparation of 7r yielded the interH,O bath and treated over 30 min with a solution of 44.6 g (0.15 mediate 1-phenylmethyl ester 6s as an oil. Saponification of 6s mol) of enol ester 4a19 in 100 mL of DMSO. The mixture was as described in method C and recrystallization of the product from stirred for an additional 45 min and then treated in one portion EtOH/hexane gave a 68% overall yield of the analytically pure with 25.0 mL (32.8 g, 0.27 mol) of 2-bromopropane. After stirring carboxylic acid 7s: mp 128-130 "C; IR (KBr) 1673, 1493,1308, at room temperature for an additional 48 h, the reaction mixture 1228 cm-'; 'H NMR (CDCl,) 6 1.50 (d, 6 H, CH(CH,),), 3.87 (9, was added to 2.5 kg of ice/H,O, acidified with 6.0 N HC1, and 3 H, OCH3), 4.97 (heptet, 1 H, CH(CH,),), 5.80 (s, 2 H, CH,), extracted with CHpC12(4 x 800 mL). The combined organic layers 6.88-7.47 (m, 8 H, A r m , 10.53 (br s, 1 H;COzH). Anal. (C,were washed with HzO (1 X 1.5 L), 5% aqueous NaHCO, (2 X HziN04) C, H, N. 1.5 L), and H 2 0 again. The extracts were dried (Na2S04)and Method C. This saponification procedure, in which the K+ evaporated to leave the product alkoxy ester 6d as a crude oil salt of the carboxylic acid product is isolated, has been previously containing some residual DMSO. This material was saponified described.ls without additional purification. Method D. 5-Chloro-3-(l-methylethoxy)-l-phenyl-1H(This procedure was also employed with diethyl sulfate as the indole-2-carboxylic Acid (72). A solution of 14.8 g (0.043 mol) alkylating agent.) Methyl l-Phenyl-3-(phenylmethoxy)-lH-indole-2- of ester 62 in 85 mL of MeOH was treated with a solution of 6.4 g (0.11 mol) of KOH in 85 mL of HzO. The mixture was stirred carboxylate (6cc). The N-alkylation procedure described in the at reflux for 3 h, cooled, and condensed to one-third of the original preparation of 7r was also employed for 0-alkylation of ester 4bb19 volume. The residue was treated with 400 mL of HzO, and the with phenylmethyl chloride. From 5.3 g (0.02 mol) of 4bb there mixture was extracted with CH2C12(3 X 250 mL). The aqueous was obtained 3.8 g (54%) of ester 6cc. A sample recrystallized layer was filtered, cooled in ice, and acidified with 6.0 N HC1. The several times from aqueous MeOH was analytically pure: mp precipitated product was filtered and washed with water to yield 117-119 "C; IR (KBr) 1725, 1453, 1374, 968 cm-'; 'H NMR 10.2 g (72%) of crude acid 72. A sample recrystallized from (CDCl,) 6 3.67 (s, 3 H, CH,), 5.27 (s, 2 H, CH2),6.90-7.83 (m, 14 EtOAc/hexane was analytically pure: mp 130 "C dec; IR (KBr) H, A r m . Anal. (C23H19N03)C, H, N. 1677, 1497, 1280, 1103 cm-'; 'H NMR (CDCI,) 6 1.48 (d, 6 H, Method E. 5-Methoxy-1 -phenyl-3-(pheny1methoxy)-1HCH(CH3)2), 4.92 (heptet, 1H, CH(CH,),), 7.00-7.70 (m, 8 H, ArH). indole-2-carboxylic Acid (7f). A solution of 201 g (0.52 mol) Anal. (C18H16C1N03)C, H, N, C1. of ester 6f in 1.0 L of MeOH was treated with a solution of 83 1-Phenyl-3-(phenylmethoxy)-lH-indole-2-carboxylic Acid g (1.48 mol) of KOH in H20. The mixture was stirred at reflux (7cc). A mixture of 11.9 g (0.033 mol) of ester 6cc in 200 mL for 3 h, cooled, and filtered, and the filtrate was added to 7.0 kg of DMSO was treated with 7.4 g (0.066 mol) of t-BuOK. The of ice/H20. Acidification with HOAc precipitated the crude mixture was stirred and heated at 65 "C for 2 h, cooled, and added product, which was filtered and washed with water to yield 174 to 2.5 kg of ice/HzO. The solution was filtered, and the filtrate g (89%) of acid 7f. A sample recrystallized from aqueous acetone was cooled in ice and acidified with 6.0 N HCl. The precipitated was analytically pure: mp 123 "C dec; IR (KBr) 1685, 1493, 1208, product was filtered and washed with water to yield 9.7 g (899'0) 698 cm-';'H NMR (CDC13)6 3.74 (s, 3 H, CH,), 5.30 (s, 2 H, CH,), of carboxylic acid 7cc. A sample recrystallized from EtOAc/ 6.78-7.57 (m, 13 H, A r m , 8.62 (br s, 1 H, C02H). Anal. (C2,hexane was analytically pure: mp 140-142 "C; IR (KBr) 1671, Hi&JOJ C, H, N. 1470, 1276, 1151 cm-'; 'H NMR (CDCl,) 6 5.42 (s, 2 H, CHJ, 5-Methoxy-3-(4-nitrophenoxy)l-phenyl-lH-indole-26.90-7.84 (m, 14 H, A r m , 8.31 (br s, 1 H, C02H). Anal. (CZ2carboxylic Acid (7g). A mixture of 15.0 g (0.050 mol) of enol Hi,N03) C, H, N. 3-Hydroxy-5-methoxy-l-phenyl-N-1H-tetrazol-5-yl-l~indole-2-carboxamide(8a). A solution of 4.4 g (0.010 mol) of (28) Finkel, M. P.; Mallard, S . P.; Thueson, D. 0.;Conroy, M. C. J . Allergy Clin. Immunol. 1988,81,313. (carbony1amino)tetrazole 8f in 125 mL of T H F was subjected to
Compound 8d (now designated CI-949) also inhibited allergic mediator release from guinea pig and human lung. In addition, 8d is active in several in vivo allergy models,28 and is currently undergoing clinical trials. Experimental Section
Indolecarboxamidotetrazoles as Antiallergy Agents
Journal of Medicinal Chemistry, 1989, Vol. 32, No. 6 1365
recrystallized an additional time as above yielded analytically pure catalytic hydrogenation in a Parr apparatus (0.30 g 20% Pd/C ester 12: mp 107-109 "C; IR (KBr) 2239 (weak), 1720,1499,1211 catalyst, 25 OC, 52 psi Hz pressure, 24 h). The mixture was filtered, cm-'; 'H NMR (CDC1,) 6 3.74 ( 8 , 3 H, CH,), 3.86 (s, 3 H, CH3), and the crude product was separated from the spent catalyst by 4.51 (s, 2 H, CH,), 6.58-7.44 (m, 8 H, ArH). Anal. (Cl7Hl6N2o3) extracting the insoluble material with warm 2-methoxyethanol. C, H, N. The original filtrate and extracts were combined and evaporated. 3-Hydroxy-5-methoxy-1-phenyl-1H-indole-2-carbonitrile Recrystallization of the residue from aqueous 2-methoxyethanol (13). A suspension of 8.4 g (0.075 mol) of t-BuOK in 200 mL of yielded 1.8 g (52%) of the analytically pure hydroxy (carbonylTHF was cooled in ice and treated over 2 h with a solution of 13.7 amino)tetrazole 8a: mp 240 "C dec; IR (KBr) 1683,1608,1497, g (0.046 mol) of ester 12 in 150 mL of THF. The mixture was 1213 cm-'; 'H NMR (MezSO-d6)6 3.78 (s, 3 H, CH3), 6.95-7.48 stirred a t room temperature for 48 h and then added to 1.1 kg (m, 8 H, A r m , 10.90 ( s , 1 H, OH or CONH). Anal. (C17H14N6of ice/HzO and acidified with HOAc. The precipitated solid was 03.HzO). Method F. 5-Methoxy-l-phenyl-3-(phenylmethoxy)-N- filtered and washed with water. Recrystallization from aqueous MeOH yielded 10.7 g (88%) of the nitrile product. A sample 1H-tetrazol-5-yl-1H-indole-2-carboxamide (8f). A mixture recrystallized an additional time as above yielded analytically pure of 5.2 g (0.014 mol) of acid 7f and 4.8 g (0.030 mol) of 1,l'nitrile 13: mp 182 "C dec; IR (KBr) 2219, 1599, 1457, 1263 cm-'; carbonylbis(1H-imidazole) in 20 mL of DMF was stirred and 'H NMR (MezSO-d6)6 3.77 (s,3 H, CH,), 6.97-7.62 (m, 8 H, Arm, heated on the steam bath for 20 min. The mixture was cooled, 10.86 (s, 1 H, OH). Anal. (C16HlzNz02) 1.7 g (0.017 mol) of 5-aminotetrazole monohydrate was added, C, H, N. 5-Methoxy-3-(l-methylethoxy)-l-phenyl-lH-indole-2and heating was continued for an additional 20 min. The cooled carbonitrile (14). Enol nitrile 13 was alkylated with 2-bromoreaction mixture was added to 250 g of ice/HzO and acidified with propane by the procedure described in method B. The crude 4.0 N HCl. The precipitated product was filtered, washed with product was purified by flash chromatography (E. Merck 9385 water, and recrystallized from aqueous DMF to yield 3.3 g (54%) SiOz; 1:l CHzClzin hexane elution) and then recrystallized from of (carbony1amino)tetrazole 8f. A sample recrystallized an adaqueous 2-PrOH. From 6.0 g (0.023 mol) of enol 13 there was ditional time as above was analytically pure: mp 212 "C dec; IR obtained 4.8 g (69%) of analytically pure alkoxy nitrile 14: mp (KBr) 1669,1596,1532, 1211 cm-'; 'H NMR (MezSO-d6)6 3.82 79-81 "C; IR (KBr) 2203,1543,1498,1262cm-'; 'H NMR (CDCI,) (s, 3 H, CH3), 5.45 (s, 2 H, CHJ, 6.93-7.71 (m, 13 H, A r m , 11.18 8 1.47 (d, 6 H, CH(CH,),), 3.86 (s, 3 H, OCH3), 4.90 (heptet, 1 (s, 1 H, CONH), 15.76 (br s, 1 H, tetrazole NH). Anal. (Cz4H, CH(CH3)2),6.97-7.58 (m, 8 H, Arm. Anal. (C19H18Nz0z) C, HzoN60J C, H, N. 5-Methoxy-3-(methylsulfonyl)-l-phenyl-N-1H-tetrazol- H, N. 5-yl- 1H-indole-2-carboxamide (8k). A solution of 1.2 g (0.0032 5-Methoxy-3-(1-methy1ethoxy)-1-phenyl-2-( LH-tetrazolFi-yl)-lH-indole (15). A mixture of 2.97 g (0.0097 mol) of nitrile mol) of (carbony1amino)tetrazole 8j in 75 mL of HzO containing 14 and 3.6 g (0.011 mol) of tri-n-butylstannyl azidezz in 35 mL 0.27 g (0.0032 mol) of NaHC03 was treated with a slurry of 2.0 g (0.013 mol) of KMnO, in 25 mL of acetone. After stirring for of DMF was stirred at reflux for 87 h. The cooled reaction mixture was evaporated, and the residue was dissolved in isopropyl ether. 2 h, the mixture was filtered through a bed of Celite filter-aid. The filtrate was cooled in ice and acidified with HOAc to preA solution of isopropyl ether saturated with gaseous HC1 was added, and the gummy precipitate that formed was removed by cipitate the sulfone product 8k,which was filtered and washed with water. Recrystallization from aqueous 2-PrOH/MeCN extracting with 1.0 N aqueous NaOH (3 X 100 mL). The comyielded 0.38 g (28%) of analytically pure sulfone 8k: mp 263 "C bined base extracts were washed with CHZClz(3 X 150 mL) and then cooled in ice and acidified with HOAc. The precipitated dec; IR (KBr) 1693,1606,1408,1216 cm-'; 'H NMR (MezSO-d6) 6 3.11 (s, 3 H, SCH,), 3.73 (s, 3 H, OCH,), 6.69-7.56 (m, 8 H, Arm, product was removed by extracting with EtOAc (4 X 100 mL). The combined organic layers were back-washed with HzO (2 X 12.71 (s, 1 H, CONH). Anal. (C18H16N604S.HzO) C, H, N. 5-Hydroxy-3-(1-methy1ethoxy)-1-phenyl-N-1H-tetrazol- 150 mL), dried (NazS04),and evaporated to a syrup which crystallized upon standing at room temperature. Recrystallization 5-yl-lH-indole-2-carboxamide (8v). A solution of 3.33 g (0.0071 mol) of (carbony1amino)tetrazole 8w in 100 mL of T H F was from hexane/EtOAc yielded 1.3 g (38%) of the analytically pure tetrazole 15: mp 162-164 "C; IR (KBr) 1606, 1496, 1252, 1066 subjected to catalytic hydrogenation in a Parr apparatus (0.30 cm-'; 'H NMR (CDCl,) 6 1.45 (d, 6 H, CH(CH3)2),3.87 (s, 3 H, g 20% P d / C catalyst, 25 "C, 20 psi H, pressure, 18 h). After OCH,), 4.90 (heptet, 1 H, CH(CH3)&,6.92-7.60 (m, 8 H, A r m , removal of the catalyst by filtration, the filtrate was evaporated. Recrystallization of the residue from aqueous MeOH/DMF 13.17 (br s, 1 H, tetrazole NH). Anal. (Cl9Hl9N5O2)C, H, N. yielded 2.0 g (74%) of the analytically pure hydroxy (carbonylBiological Methods. Human Basophil Test. The basophil amino)tetrazole 8v: mp 243 "C dec; IR (KBr) 1684, 1603, 1499, procedure has been previously de~cribed.8'~ In brief, whole human 1199 cm-'; 'H N V R (MezSO-d6)8 1.43 (d, 6 H, CH(CH,),), 4.71 blood was obtained from well-characterizedallergic donors. After (heptet, 1 H, CHICH,),), 6.81-7.71 (m, 8 H, A r m , 9.33 (s, 1 H, sedimentation of the red cells, the leukocytes were removed, washed, and suspended in buffer solution. Cells were preincubatd OH), 11.35 (s, 1 H, CONH), 16.05 (br s, 1 H, tetrazole NH). Anal. with the test compound, then challenged with anti-IgE. The (C19H18N603*0.5H20)C, H, N. released histamine was quantitated by using an automated Method G. 5-Chloro-3-(1-methy1ethoxy)-1-phenyl-N-1Hfluorometric assay. The percent inhibition of histamine release tetrazol-5-yl-lH-indole-2-carboxamide (82). A mixture of 8.0 was calculated by comparison of the values from the test drugg (0.024 mol) of acid 72 and 4.5 g (0.028 mol) of 1,l'-carbonyltreated cells with that of nondrug controls similarly challenged bis(1H-imidazole) in 150 mL of MeCN was stirred a t reflux for with anti-IgE. As a minimum, each test compound was screened 90 min. The mixture was cooled and treated with 2.5 g (0.029 in triplicate at drug concentrationsof 33 and 10 pM. An inhibition mol) of anhydrous 5-aminotetrazole followed by 8.2 mL (6.0 g, 0.059 mol) of triethylamine. After heating for an additional 16 of 1 2 5 % a t 33 pM was arbitrarily defined as inactive. Where an IC50 value was determined, additional experiments were h, the mixture was cooled, added to 500 g of ice/HzO, and acidified conducted with threefold concentrations from 1 to 100 pM. with HOAc. The precipitated product was filtered, washed with water, and recrystallized from aqueous MeCN to yield 5.8 g (60%) Guinea P i g Chopped L u n g Test. Detailed procedures for of the analytically pure (carbony1amino)tetraole 82: mp 228 "C this test have also been published.16 Washed aliquots of minced dec; IR (KBr) 1676,1496,1280,1100 cm-'; 'H NMR (MezSO-d6) lung from guinea pigs previously sensitized with ovalbumin were 8 1.37 (d, 6 H, CH(CH,),), 4.74 (heptet, 1 H, CH(CH3)a, 7.15-7.56 incubated (in triplicate) with the test compound or a control buffer (m, 7 H, Arm, 7.92 (d, 1 H, 64 Arm, 11.61 (s, 1 H, CONH), 16.10 solution and then challenged with ovalbumin antigen. Histamine (br s, 1 H, tetrazole NH). Anal. (C19H17ClN60z) released into the supernatant fluids as well as that remaining in C, H, N, C1. the lung tissue was quantified by an automated fluorometric M e t h y l 2-[(Cyanomethyl)phenylamino]-5-methoxytechnique. The effect (percent inhibition) of drug on antigenbenzoate (12). A mixture of 14.2 g (0.050 mol) of carboxylic acid induced histamine release was calculated and corrected for 11,198.0 g (0.058 mol) of anhydrous KzC03,and 6.0 mL (8.0 g, spontaneous release from buffer-treated control tissues. Assays 0.063 mol) of MeZSO4in 400 mL of MeCN was stirred a t reflux were performed a t drug concentrations of 0.75, 7.5, and 75 pM for 21 h. The cooled mixture was filtered, and the insoluble in order to calculate IC,o values. material was washed with fresh MeCN. The combined filtrates were evaporated, and the residue was recrystallized from aqueous H u m a n Chopped L u n g Test. Portions of grossly normalappearing human lung obtained during lobectomy for carcinoma MeOH to yield 13.7 g (92%) of the ester product. A sample
1366
J . Med. Chem. 1989, 32, 1366-1370 buffer at 37 'C. After a 10-min incubation in Tyrode's buffer, test drug or vehicle was added, and 10 min later, the tissue was incubated with anti-IgE in a final dilution of 3:lOOO. After another 30-min incubation, samples of the supernatant were removed for assay. Histamine was assayed as described above in the guinea pig chopped lung test.
were placed in Tyrode's buffer, dissected free of larger bronchioles and blood vessels, and then chopped with scissors into 25-75-mg fragments. The fragments were washed and then stored overnight in Tyrode's buffer at room temperature. Before use the next day, the tissue was again washed with buffer. Portions of lung tissv-e (about 400 mg) were placed in each of a series of vials containing
The Role of Position 4 in Angiotensin I1 Antagonism: A Structure-Activity St udyt J. Samanen,*p' T. Cash,' D. Narindray,' E. Brandeis,' T. Yellin,' and D. Regolii S m i t h Kline and French Laboratories, Peptide Chemistry Department, 709 Swedeland Road, P.O. Box 15839, King of Prussia, Pennsylvania 19406-0939, and the Department of Pharmacology, University of Sherbrooke, Quebec, Canada. Received August 3, 1988
A number of [Sar1,(pX)Phe4]-ANGI1 and [Sar1,(pX)Phe4,11ea]-ANG I1 analogues were prepared. A good correlation between pX structure in [Sar1,(pX)Phe4]-ANGI1 and antagonist activity could not be found. However, the data suggest a general trend: Position 4 para substituents that are hydrophilic and capable of donating a hydrogen atom in a hydrogen bond promote agonist activity, while para substituents that are hydrophobic and incapable of donating a hydrogen atom promote antagonist activity. These properties were found to be optimal in the p-chloro substituent. The resulting analogue [Sar1,(pC1)Phe4]-ANGI1 is a potent ANG I1 antagonist in vivo. The pX substituents that promote antagonist activity in the [Sar1,(pX)Phe4]-ANGI1 series were unfavorable in [Sar1,(pX)Phe4,11e8]-ANG I1 analogues. ANG I1 analogues that are antagonists by virtue of an alteration in position 8 require a position 4 egonist side chain. Concurrent modifications of positions 4 and 8 do not give rise to potent antagonists with reduced partial agonist activity.
Among the first reported' antagonists of angiotensin I1 was the analogue [Phe4,Tyr8]-ANG I1 3293(Table I ) ' V ~ - ' ~ which contained an alteration of the tyrosine in position 4. Other weak antagonists were reported shortly after: [(pF)Phe4-ANGI1 4' and [Phe4]-ANG I1 l4 (Table I). In that same period antagonists of much greater potency were discovered by alteration of the 8-position: [Ala8]-ANGI1 9: [Leu*]-ANG I1 11,'' [Ile8]-ANGI1 12,3and [Cys8]-ANG 11 10.3 Substitution of sarcosine for aspartic acid in position 1 was later shown to enhance antagonist action by blocking aminopeptidase action and increasing antagonist affinity12 as shown in the potent antagonists [Sar',Ala8]-ANG I1 139 and [Sarl,Ile*]-ANG I1 14.12 Although the development of [Sar1,X8]-ANGI1 antagonists continued,13investigations of [Sar',X4]-ANG I1 antagonists were not reported until recently. This may have been due to the lower potency of the [X4]-ANGI1 antagonists compared to the [X8]-ANG I1 antagonists (Table I). [Sar',(SAcm)Phe4]-ANG I1 5 (Table I) was recently described to be a potent ANG I1 antagonist by Escher et al.14 and [Sar',(OMe)Tyr4]-ANG I1 6, also a potent antagonist, Table I, was recetly reported by Goghari et aL6 In previous work5J4 Escher has shown that hydrogen bonding and the inductive effects (electronegativity) of the para substituent are important for optimal agonist activity of position 4 analogues of [Sar'l-ANG 11. We have been pursuing the structure-antagonist activity relationship of [Sar1,X4]-ANGI1 antagonists. This paper describes our attempt to optimize the activity of position 4 antagonist 'The abbreviations for natural amino acids and nomenclature for peptide structures follow the recommendations for peptide structures of the IUPAC-IUB commission on Biochemical Nomenclature ( J . Biol. Chem. 1971, 247, 977). Abbreviations for nonnative amino acids include Bph = p-(dihydroxybory1)phenylalanine, (0Me)Tyr = 0-methyltyrosine, (pF)Phe = p fluorophenylalanine, (SAcm)Phe = p - [(acetamidomethy1)thiolphenylalanine. Other abbreviations in this paper include TEA = triethylamine, TFA = trifluoroacetic acid, DCC = N,N'-dicyclohexylcarbodiimide. Smith Kline and French Laboratories. g University of Sherbrooke.
*
0022-2623/89/1832-1366$01.50/0
analogues. The partial agonist activity of [Sar1,Ala8]-ANGI1 13 and other position 8 modified antagonists has precluded their use as antihypertensive agents13 in humans. Structural modifications that could reduce such partial agonist activity could improve the therapeutic potential of ANG I1 antagonists. Since antagonist action may be obtained by modification of either position 4 or position 8, both residues must be responsible for receptor stimulation. Hence, modifications of both positions 4 and 8 in the same peptide may result in the creation of an ANG I1 antagonist devoid of agonist activity. This possibility was explored in the present study. (1) Khairallah, P. A.; Toth, A.; Bumpus, F. M. J . Med. Chem. 1970, 13, 181-184. (2) Marshall, G. R.; Vine, W.; Needleman, P. Proc. Natl. Acad. Sci. U.S.A. 1970, 67, 1624-1630.
(3) Needleman, P.; Johnson, E. M.; Vine, W.; Flannigan, E.; Marshall, G. R., In Chem. and Biol.Peptides, Proc. 3rd Amer. Peptide Symp., Meienhofer, J., Ed.; Ann Arbor Science Publishers: Ann Arbor, MI, 1972; pp 501-507. (4) Park, W. K.; Regoli, D.; Rioux, F. Br. J. Pharmacol. 1973, 48, 288-301. (5) Escher, E.; Bernier, M.; Parent, P. Helu. Chim. Acta 1983, 66, 1355-1365. (6) Goghari, M. H.; Franklin, K. J.; Moore, G. J. J . Med. Chem. 1986, 29, 1121-1124. (7) Turker, R. K.; Yamamoto, M.; Khairallah, P. A.; Bumpus, F. M. Eur. J . Pharmacol. 1971, 15, 285-291. (8) Regoli, D.; Park, W. K.; Rioux, F. Pharm. Rev. 1974, 26, 69-123. (9) Pals, D. T.; Denning, G. S., Jr.; Keenan, R. E. Kidney Int. 1979, 15, S-74-10. (10) Turker, R. K. Hall, M. M.; Yamamoto, M.; Sweet, C. S.; Bumpus, F. M. Science 1972, 177, 1203-1205. (11) Reaoli. D.: Park. W. K.; Rioux, F.; Chan, C. S. Rev. Can. Biol. 1971, 30, 319-329. (12) Regoli, D.; Park, W. W. Can. J . Physiol. Pharmacol. 1972, 50, 99-112. (13) Bumpus, F. M.; Khosla, M. C. In Hypertension: Physiopathology and Treatment; Genest, J., Koiw, E., Kuchel, O., Eds.; McGraw-Hill Book Co.: New York, 1977; pp 183-201. (14) Escher, E.; Bernier, M. In Peptides 1980, Proc. 16th Eur. Peptide Symp.; Brunfeldt, K., Ed.; Scriptor: Copenhagen, 1981; pp 457-462.
@ 1989 American Chemical Society
